1. Field of the Invention
The present invention relates to a semiconductor device which comprises a plurality of semiconductor elements, such as computers, semiconductor image sensors, etc., and a process for fabricating the same.
2. Description of the Related Art
Examples of the known technology for this field include the methods illustrated in FIGS. 8 to 10. Referring to a prior art device illustrated in FIG. 8, a plurality of semiconductor chips 1 are adhered and fixed on a single alumina substrate 2, and the plurality of semiconductor chips 1 are electrically connected one another by gold-wire bonding 18 between the pads 5 on the semiconductor chips 1 and the copper interconnection 6 on the alumina substrate 2. According to another prior art technology with reference to FIG. 9, the active plane of the semiconductor chip 1 having a solder bump 19 previously formed thereon is opposed to the alumina substrate 2 having thereon a copper interconnection 6, and the plane is heated to about 220.degree. C. to melt and adhere the copper interconnection 6 to the solder bump 19. In this manner, the desired electrodes of the plurality of semiconductor chips 1 are electrically connected to obtain the semiconductor device. In another prior art device with reference to FIG. 10, a semiconductor chip 1 having thereon a gold bump 21 is opposed to a tin lead 20 being adhered to a polyimide film 13, and is heated together with the polyimide film to about 400.degree. C. to eutectically join the gold bump 21 on the semiconductor chip 1 with the tin lead. Thus, a plurality of semiconductor chips 1 have been electrically connected by any of the aforementioned processes.
The prior art processes described above are provided for electrically connecting a plurality of semiconductor chips to one another, however, following problems were found yet to be unsolved. In the method of wire bonding the plurality of semiconductor elements with reference to FIG. 8, the use of a wire bonding machine creates several problems. Due to the limitations of the wire bonding machine, a long distance w is necessary for drawing the wire. Thus, at least a distance of 2 w is necessary between two adjacent semiconductor elements, and, moreover, a height of h is required for drawing out the wire. Consequently, the semiconductor device composed of a plurality of semiconductor elements becomes voluminous and thick. Furthermore, since about 0.25 seconds per wire is necessary for the connection, the total process consumes considerable time. This leads to the increase in production cost. Referring to the process comprising connecting a plurality of semiconductor elements via the solder bumps with reference to FIG. 9, the elements are pulled and connected one another by the surface tension of the solder. With increasing size of the semiconductor element, however, warping and thermal deformation occur on the semiconductor elements to generate bumps which cannot be brought into contact with the neighboring bumps. Another prior art process with reference to FIG. 10 is unfeasible to connect the semiconductor elements having a large number of pads, because the capacity of producing the leads is limited to about 400 pins. Moreover, none of the aforementioned processes with reference to FIGS. 8, 9, and 10 can achieve the connection of semiconductor elements having a pitch between pads as short as about 0.1 mm or even narrower.